Steam generator and regenerative air heating system therefor



Oct. 25, 1966 H. J. BLASKOWSKI 3,280,793

STEAM GENERATOR AND REGENERATIVE AIR HEATING SYSTEM THEREFOR Filed Dec. 29, 1964 4 Sheets-Sheet l F'IGJ INVENTOR HENRY .J- BLASKOWSKI ATTORNEY Oct. 25, 1966 H. J. BLASKOWSKI 3,280,798

STEAM GENERATOR AND REGENERATIVE AIR HEATING SYSTEM THEREFOR Filed Dec. 29, 1964 4 Sheets-Sheet 2 F IGLZ j INVENTOR HENRY J. BLASKOWSKI BY [id m /4( ATTORNEY Oct. 25, 1966 H. J. BLASKOWSKI 3,280,798

STEAM GENERATOR AND REGENERATIVE AIR HEATING SYSTEM THEREFOR Filed Dec. 29, 1964 4 Sheets-Sheet 3 FICS-4 INVENTOFQ HENRY J BLASKOWSKI BY (OZ/n M ATTORNEY Oct. 25, 1966 H. J. BLASKOWSKI 3,280,798

STEAM GENERATOR AND REGENERATIVE AIR HEATING SYSTEM THEREFOR Filed Dec. 29, 1964 4 Sheets-Sheet 4 FIC5-5 INVENTOR HENRY J- BLASKOWSKI BY g 4 1,0224.

ATTORNEY United States Patent 3 280,798 STEAM GENERATOR AND REGENERATIVE AIR HEATING SYSTEM THEREFOR Henry J. Blaskowslri, Simshury, Conn., assignor to Combustion Engineering, Inc., Windsor, C0nn., a corporation of Delaware Filed Dec. 29, 1964, Ser. No. 421,778 4 Claims. (Cl. 122-1) This invention relates generally to large capacity vapor generators and has particular relation to such a. vapor generator having included as a portion there-of an improved heat exchange system for reducing the temperature of the combustion gases discharged from the generator and for heating the air that is supplied to the furnace of the generator for the purpose of supporting combustion therein.

In accordance with the invention this heat exchange system utilized with the vapor generator is of such design and construction as to be of minimum cost and require a minimum floor space while at the same time being highly efficient in its operation thereby lowering the over-all cost of the vapor generator installation and tending to decrease the cost of power produced by means of the vapor generator.

The organization of the invention utilizes a vapor generator which has a furnace into which fuel is introduced and burned with the fuel being any of the well-known fuels conventionally employed in high capacity steam generators such as pulverized coal, *oil and gas. The combustion gases produced as a result of burning this fuel in the furnace are conveyed from the furnace through a gas pass with these gases traversing various heat exchange surface in the gas pass and eventually being introduced into a stack for discharge to atmosphere. Combustion supporting air is supplied to the furnace to support the burning of the fuel therein, and the unit may be of the induced draft type wherein a fan is positioned at the outlet or gas discharge of the generator to draw combustion supporting air into the furnace or it may be of the forced draft type wherein the fan is positioned to force the combustion supporting air into the furnace. If desired, both a forced draft and an induced draft fan may be utilized.

It is desired to lower the temperature of the combustion gases egressing from the furnace to a relatively lower value in order that the efficiency of operation may be at an optimum. A limiting factor in thus lowering the temperature of the gases is the requirement that they be maintained above the dew point in order that moisture, which may be highly corrosive, will not form on the surfaces contacted by this gas.

It is further desired, for optimum operating efficiency, to heat the combustion supporting air that is introduced into the furnace. The system in accordance with the present invention for heating the combustion supporting air utilizes a tubular heat exchanger in the air duct at a location adjacent the furnace. Hot liquid, preferably high pressure water, is conveyed through this heat exchanger. After traversing this heat exchanger this liquid is conveyed through a tubular heat exchanger located adjacent the discharge portion of the gas pass leading from the furnace. In one embodiment of the invention these two heat exchangers are connected into a closed system with pump means being provided to force the liquid through a circuit that includes these heat exchangers. A bypass is provided for the heat exchanger located in the gas duct with this bypass forming a part of this circuit and with there being a control valve in this bypass regulated by a temperature responsive device that responds to the temperature of the gas egressing from the duct leading from the furnace. In another embodiment of the invention the vapor generator is of the forced circulation type with there being a pump means operative to convey water from the steam and water drum of the generator through tubes that line the furnace. The circuit for the heat exchangers in the air duct and the gas pass is such that a portion of the output of this pump is conveyed first through the heat exchanger in the air duct where heat is imparted from the boiler water to the air traversing said heat exchanger and thereafter the boiler water is conveyed through the heat exchanger in the gas duct where heat is imparted from the gas traversing this heat exchanger to this water. The water is then mixed with the remainder of the output of the pump and forced through the tubes that line the furnace of the vapor generator. Control means are provided to control the amount of water forced through the heat exchanger with this control means responding to the temperature of the gas leaving the gas pass such as to maintain this temperature above the dew point.

In order to achieve the optimum economy with the system of the invention, it is essential that the heat exchangers in both the air duct and the gas pass be of particular construction with the tubes being within a particular size range and being provided with spiral fins of particular dimension and with a particular material being employed for the tubes and fins. With the heat exchangers constructed in accordance with the invention their size and cost is reduced to a value such that the over-all system is of minimum cost and occupies a minimum amount of space thereby achieving maximum benefits with an over-all optimum operation.

It is accordingly an object of the invention to provide an improved vapor generator that has a furnace fired with a suitable fuel and an improved system for heating combustion supporting air supplied to the furnace of the generator and for absorbing heat from the gases that egress from the furnace.

A still further object of the invention is to provide such an improved vapor generator organization wherein this system utilizes tubular heat exchangers over which the combustion supporting air and the gases from the furnace are conveyed with a liquid being forced through these heat exchangers.

A still further object of the invention is to provide such an improved vapor generator organization wherein the heat exchangers utilize spiral finned tubes and are of particular design wherein optimum cost savings are realized.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawings wherein:

FIGURE 1 is a vertical transverse section, diagrammatic and fragmentary in nature, disclosing a high capacity vapor generator embodying the present invention;

FIGURE 2 is a transverse section taken generally along line 22 of FIGURE 1;

FIGURE 3 is an enlarged detailed elevational view of the support arrangement for the heat exchanger in the air duct with this view illustrating the subject matter within the circle identified as 33 of FIGURE 1;

FIGURE 4 is a view similar to that of FIGURE 1 but showing another form of the invention;

FIGURE 5 is a set of curves wherein temperature is plotted against heat pickup and showing that the ratio of the surfaces of the heat exchangers in the gas pass and the air duct are such as to obtain a design utilizing minimum surface with optimum heat exchange;

FIGURE 6 is a detailed View of the spiral finned tube construction of which the heat exchangers that form a part of the invention are made; and

FIGURE 7 is a fragmentary view showing the staggered disposition of the spiral finned tubes that make up the heat exchangers.

Referring now to the drawings, wherein like reference characters are used throughout to designate like elements, the illustrative and preferred embodiment of the invention as depicted therein includes the furnace 10 into which fuel and combustion supporting air are introduced through the burners 12 with these burners being of the general construction shown and described in US. Patent 2,697,422, issued on December 21, 1954 to W. H. Armacost. The combustion gases produced by the burning of fuel in the furnace 10 pass up through the furnace and then down through the gas pass 14 as indicated by the arrow 16. Various heat exchange surfaces such as superheater surface, economizer surface and the like is disposed within the gass pass 14. The gases pass down through this gas pass and through the outlet portion 18 being conveyed therefrom to a stack or the like for discharge to atmosphere.

The furnace of the vapor generator 10 is preferably lined with steam generator tubes and water is conveyed from the steam and Water drum 20 via downcomer 22 to the inlet header 24 with this water then passing up through the furnace tubes and the steam and water mixture produced therein discharged into the drum 20.

In the illustrative embodiment, combustion supporting air is forced through duct 26 via the forced draft fan 28 entering the furnace 10 through the burners 12. There are air ducts 26 located on each side of the furnace, as shown in FIGUREZ, and within these air ducts are positioned the heat exchangers 30 and 32. These heat exchangers are connected into a system that is efiective to heat the combustion supporting air that is introduced through the burners 12 and for this purpose the heat exchangers are connected with outlet header 34 and inlet header 36. Fluid is forced through the heat exchangers by means of pump 38 which has its inlet connected by conduit 40 to the outlet header 34. The outlet of this pump is connected by conduit 42 to the inlet header 44 of the heat exchanger 46 positioned adjacent the discharge end of gas duct 14 so that the hot combustion gases flow thereover. The pump forces the liquid heat exchange fluid through the heat exchanger 46 to the outlet header 48. There is connected with this outlet header an expansion tank 50 which has contained in the upper region thereof nitrogen gas, and also connected with the header 48 is the conduit 52 which is connected with the inlet header 36 of heat exchangers 30 and 32. The liquid medium within this circuit is preferably high pressure water, although other fluids such as biphenyl and arclor and the like may be used. The pump 38 is eifective to force the water through this circuit with heat being imparted thereto during traversal of the heat exchanger 46 and with heat being imparted from this fluid to the combustion supporting air during traversal of the heat exchangers 30 and 32.

In order that the temperature of the combustion gases exiting from gas duct 14 at the outlet region 18 may be regulated so that they are maintained above the dew point, there is provided the temperature responsive device 54 positioned to respond to the temperature of these gases. This device 54 in turn controls the valve 56 in bypass 58 connected in bypass relation with the heat exchanger 46. Thus, through manipulation of the valve 56 the amount of fluid flowing through the heat exchanger 46 can be regulated and thus in turn the temperature of the gases from duct 14 can be regulated.

The heat exchangers within the duct 26 and the heat exchanger 46 at the outlet of gas pass 14 are comprised of sinuously bent tubes with these tubes having portions that extend transversely across the duct or gas pass with these portions being vertically disposed and interconnected via return bends as best shown in FIGURE 3. The tubes which make up these heat exchangers and which may be identified as 60 (FIGURE 3) are provided with spiral fins, and as previously mentioned the construction and design of these heat exchangers are such as to provide for the greatest possible cost reduction. In this connection it is essential that the tubes and fins be of carbon steel and that the tubes have an outside diameter within the range of to 1% inches. The fins have a width of between /2 to inch and a thickness of between .02 and .03 inch. The spiral fins are wound with a pitch such that there are six to eight turns per inch of tube and the tubes are disposed in an array such that alternate rows are staggered with FIGURES 6 and 7 showing the fins 62 as thus applied to the tubes and showing the tubes in their staggered array.

For economy of construction and support it is necessary that the tubular elements that make up the heat exchangers 30, 32 and 46 be of the construction previously mentioned with vertically extending tube portions interconnected by return bends, since with this design the tube bundles that form the heat exchangers may be supported as disclosed in FIGURE 3 with support rods 62 being connected with the upper region of the tube runs, these rods in turn being supported from structural member 64. This member 64, which is contained Within the gas-tight housing 66, is supported from the structural steel member 68 by means of the hanger rods 70 that extend down through bellows type seals 72.

With this arrangement optimum economy of both space occupied by the vapor generator and of cost of the air heating system are realized.

The ratio of the surface of the heat exchanger 46 and the heat exchangers in the air ducts is such that the temperature of the water leaving the former heat exchanger and entering the latter heat exchangers is midway between the temperature of the combustion gases initially traversing heat exchanger 46 and the temperature of the air leaving the heat exchangers 30 and 32 while the temperature of the water leaving heat exchangers 30 and 32 and entering heat exchanger 46 is midway between the temperature of the gases as they leave the heat exchanger 46 and the temperature of the air entering the heat exchangers 30 and 32. This is shown in the curve of FIGURE S wherein heat pickup is plotted as the abscissa against temperature as the ordinate. This curve shows that the temperature of the water entering and leaving the air and gas heat exchangers lies generally midway between the curve representing the temperature of the gas as it passes through the heat exchanger 46 and the temperature of the air as it passes through the heat exchangers 30 and 32.

The organization of FIGURE 4 is generally similar to FIGURE 3 with the exception that the vapor generator of FIGURE 4 is of the forced circulation type with pump 74 forcing boiler water into header 24 and up through the tubes that line the Walls of the furnace. This pump 74 is also effective to force the boiler water through the heat exchangers 30' and 32 in the air duct 26 and through the heat exchanger 46 in the duct 14. For this purpose there is connected with the outlet conduit 76 of pump 74 the conduit 78 which connects with the inlet header 36 of heat exchangers 30 and 32. The outlet header 48 of heat exchanger 46 is connected by means of conduit 80 with header 24. Valves 82 are provided in the c0nduits 76 and 78 respectively in order to control the portion of the output pump 74 that passes through the heat exchangers 30, 32 and 46 and the portion that passes directly via conduit 76 to the header 24. In the header 24 the water egressing from heat exchanger 46 through conduit 80 is mixed with the water conveyed directly to the header through conduit 76 and this mixture is then forced up through the tubes that line the furnace walls. Valves 82 are controlled by the temperature responsive device 54 in a manner to control the flow through the heat exchanger 46 to maintain the temperature of the gases egressing from heat exchanger 46 above their dew point.

While I have illustrated and described a preferred embodiment of my invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall Within the purview of my invention.

What I claim is:

1. In a vapor generating plant having a furnace with firing means, duct means through which combustion supporting air is supplied to the furnace, a gas pass extending from the furnace, a system for supplying preheated combustion supporting air to the furnace and for reducing the temperature of gases in said gas pass comprising a first tubular heat exchanger in said pass, a second tubular heat exchanger in said duct means, means circulating a fluid through said first heat exchanger and then through said second heat exchanger, a bypass for bypassing a portion of said fluid around said first heat exchanger, control means in said bypass, means responsive to the temperature of the gases in the duct downstream of said first heat exchanger to control said control means, said first and said second tubular heat exchangers having portions extending transversely of said duct and gas pass, respectively, and being comprised of sinuously bent carbon steel tubes assembled into a bundle and interconnected by U-bends, said tubes having an outside diameter of '%s to 1% inches and having disposed thereon spiral fins /2 to 4 inch Wide and .02 to .03 inch thick with the pitch of the fins being such as to provide six to eight turns per inch of tube.

2. In a vapor generating plant having a furnace with firing means, duct means through which combustion supporting air is supplied to the furnace, a gas pass extending from the furnace, a system for supplying preheated combustion supporting air to the furnace and for reducing the temperature of gases in said gas pass comprising a first tubular heat exchanger in said gas pass, a second tubular heat exchanger in said duct means, means circulating a fluid through said first heat exchanger and then through said second heat exchanger, a bypass for bypassing a portion of said fluid around said first heat exchanger, control means in said bypass, means responsive to the temperature of the gases in the duct downstream of said first heat exchanger to control said control means, said first and said second tubular heat exchangers having portions extending transversely of said duct and gas pass, respectively, and being comprised of sinuously bent carbon steel tubes assembled into a bundle and interconnected by U-bends, said tubes having an outside diameter of "A; to 1% inches and having disposed thereon spiral fins /2 to inch wide and .02 to .03 inch thick with the pitch of the fins being such as to provide six to eight turns per inch of tube, the ratio of surface of the two heat exchangers being such that at maximum continuous rating of the generating plant the temperature of the fluid entering said second heat exchanger is of a value approximately midway between the temperature of the gas entering and the air leaving said first and second heat exchangers, respectively, and the temperature of the fluid entering said first heat exchanger is of a value approximately midway between the temperature of the gas leaving and the air entering said first and second heat exchangers, respectively.

3. In a vapor generating plant having a furnace lined with tubes, a gas pass extending from the furnace, pump means operative to force heated boiler water through said tubes, duct means through which combustion supporting air is supplied to the furnace, a system for supplying preheated combustion supporting air to the furnace and for reducing the temperature of gases in said gas pass comprising a first tubular heat exchanger in said pass, a second tubular heat exchanger in said duct means, means directing a portion of the output of the pump means serially first through said second and then through said first heat exchanger, means mixing this portion with the remainder of the pump output and directing the mixture through the furnace tubes, control means operative to adjustably control the portion of the output of said pump that traverses said heat exchanger, means responsive to the temperature of the gases in said gas pass operative to regulate said control means, said first and second tubular heat exchangers having portions extending transversely of said duct and gas pass, respectively, and being comprised of sinuously bent carbon steel tubes assembled into a bundle and interconected by U-bends, said tubes having an outside diameter of A; to 1% inches and having disposed thereon spiral fins /2 to inch wide and .02 to .03 inch thick with the pitch of the fins being such as to provide six to eight turns per inch of tube.

4. In a vapor generating plant a furnace having firing means associated therewith, duct means through which combustion supporting air is supplied to the furnace, gas passageway means extending from the furnace and conveying combustion gases generated in the furnace, a system for supplying preheated combustion supporting air to the furnace comprising a first tubular heat exchanger means in said passageway, second tubular heat exchanger means in said duct means, means passing fluid through said two heat exchanger means in series, control means to regulate the flow of fluid through said first tubular heat exchanger means, means responsive to the temperature of the gases in the duct downstream of said first tubular heat exchanger means to regulate said control means, said first and said second tubular heat exchanger means each being comprised of sinuously bent carbon steel tubes assembled into a tube bundle and having legs or portions extending transversely of the direction of the flow of the gaseous medium flowing thereover, said tubes having disposed thereon spiral fins also comprised of carbon steel.

927,870 5/1947 France. 931,632 11/1947 France.

References Cited by the Applicant FOREIGN PATENTS 5/1934 Germany. 12/1949 Great Britain.

CHARLES J. MYHRE, Primary Examiner. 

1. IN A VAPOR GENERATING PLANT HAVING A FURNACE WITH FIRING MEANS, DUCT MEANS THROUGH WHICH COMBUSTION SUPPORTING AIR IS SUPPLIED TO THE FURNACE, A GAS PASS EXTENDING FROM THE FURNACE, A SYSTEM FOR SUPPLYING PREHEATED COMBUSTION SUPPORTING AIR TO THE FURNACE AND FOR REDUCING THE TEMPERATURE OF GASES IN SAID GAS PASS COMPRISING A FIRST TUBULAR HEAT EXCHANGER IN SAID PASS, A SECOND TUBULAR HEAT EXCHANGER IN SAID DUCT MEANS, MEANS CIRCULATING A FLUID THROUGH SAID FIRST HEAT EXCHANGER AND THEN THROUGH SAID SECOND HEAT EXCHANGER, A BYPASS FOR BYPASSING A PORTION OF SAID FLUID AROUND SAID FIRST HEAT EXCHANGER, CONTROL MEANS IN SAID BYPASS, MEANS RESPONSIVE TO THE TEMPERATURE OF THE GASES IN THE DUCT DOWNSTREAMS OF SAID FIRST HEAT EXCHANGER TO CONTROL SAID CONTROL MEANS, SAID FIRST AND SAID SECOND TUBULAR HEAT EXCHANGERS HAVING PORTIONS EXTENDING TRANSVERSELY OF SAID DUCT AND GAS, RESPECTIVELY, AND BEING COMPRISED OF SINUOUSLY BENT CARBON STEEL TUBES ASSEMBLED INTO A BUNDLE AND INTERCONNECTED BY U-BENDS, SAID TUBES HAVING AN OUTSIDE DIAMETER OF 7/8 TO 1 1/4 INCHES AND HAVING DISPOSED THEREON SPIRAL FINS 1/2 TO 3/4 INCH WIDE AND .02 TO .03 INCH THICK WITH THE PITCH OF THE FINS BEING SUCH AS TO PROVIDE SIX TO EIGHT TURNS PER INCH OF TUBE. 